LED structure with a dynamic spectrum and a method

ABSTRACT

An integrated LED structure and a method of adjusting the emission spectrum of an integrated LED structure, for photobiological process. The structure comprises a substrate; a plurality of optically isolated and electrically non-independent light emission areas integrated on the substrate; a light emitting semiconductor source of a first type mounted in the emission area(s); a light emitting semiconductor source of a second type mounted in the emission area(s); an electrical circuit layer for connecting the said light emitting semiconductor sources in serial fashion for each emission area; and wavelength conversion materials. The emission areas are controlled with a common electrical drive current, and the emission output can be tuned by adjusting the common current value, to enable use of one luminaire for a large variety of biomass growing applications.

FIELD OF INVENTION

The present invention relates to artificial lighting arrangements andmethods used in agriculture, horticulture and in biomass growingindustry. In particular, the present invention relates to the field ofoptoelectronics and photobiology. The present invention relates to useof an integrated LED structure and a method in grow lights.

BACKGROUND ART

Greenhouse industry is experiencing an era of rapidly advancingtechnologies for artificial illumination. LED based luminaires haveentered commercial use as grow lights relatively recently. HPS andconventional arc light sources are now moving aside and more efficientLED luminaires are emerging into markets including advancedfunctionalities e.g. integrated pest management (Vänninen et al., 2012).

However, the potential modes of LEDs for illuminating plants are stillrarely fully optimized. Currently used LED based luminaires still sufferlow efficiency and provide emission spectra not well overlapping withthe absorption spectra of photobiological processes such asphotosynthesis. Over-exposing of plants with high intensity sources andlack of advanced control modes such as pulsed illumination are stilltopics not fully researched or solved in practice. A LED spectrum can bematched with photobiological requirements to enhance plants' growth andto increase the total organic output i.e. the harvested volume of agreenhouse products e.g. tomatos or lettuce.

Photobiological requirements are mainly defined by the absorptionspectrum of the photosynthesis and other photobiological processes inquestion.

There is also a need to meet the timing requirements of the illuminationwhen operating with a pulsed light. The timing requirement arises fromthe chlorophyll B excitation and electron transfer delay to thechlorophyll A associated process and the potential to optimize theenergy usage for driving the photosynthesis. Other natural parametersthat account for the illumination requirements include e.g. partialpressure of carbon dioxide, irrigation level of soil, temperature andtype of canopy. Other requirements that constitute to the requiredillumination spectrum may arise e.g. from marketing motives to growvegetables with certain skin colors or the need to enhance the product'snutrition content or other effective substance.

Different plants and biomass applications require slightly differingtype of illumination conditions to reach optimal growth. This inducesgreenhouse industry to invest on many types of artificial grow lights.It is the objective of the disclosed invention to provide an integratedLED structure with adjustable emission characteristics to meet thedifferent requirements of various biomass growing applications.

A good example is e.g. the growth of red and black soybeans. Accordingto CN103947470A and CN103947469 particular light spectrum conditions arepreferred for optimum growth of red and black soyabeans, with roughblue, red, and yellow spectrum band ratios being 3:1:5 and 4:3:3respectively, demonstrating the need for adjustable spectrum type lightsource to enable one artificial grow light to be used with a variety ofdifferent plants. Similarly for example tomato plant and spruce requirequite different type of light to grow efficiently. The required spectrumcomponents also vary between different growing cycles of a same plante.g. during vegetation phase blue rich light is preferred, and floweringand fruit grow phases are typically connected with red rich light.Another requirement for adjusting the spectrum of the grow light is theneed to grow e.g. vegetables with varying skin colors of e.g. bellpaprika for marketing purposes or for enhancing certain nutritioncomponents in the paprika fruit.

A grow light with adjustable spectrum would also allow newfunctionalities not yet fully exploited in the greenhouse industry. Forexample it is known that a pre-harvesting treatment of kale affectsstrongly on the nutrition content (Carvalho et al., 2014; Lefsrud etal., 2008). Another example is the UV flash-treatment of cultivatedmushrooms prior harvesting or post harvesting to enrich their vitamin Dcontent (Beelman et al., 2009).

Another example of potential benefits of a source with an adjustableemission spectrum becomes apparent when considering biomass growthapplications such as algae (Nicklish, 1998). The absorption spectrumshifts from around 680 nm peak towards lower wavelength peak around 630nm when the photoperiod becomes shorter. Similar shift in absorbance isdocumented in the literature (Eytan, 1974). The ratio of chlorophyll Aand chlorophyll B concentration has been shown to change in time whenplant is subjected to continuous illumination as e.g. in case of RedKidney bean plants (Argyroudi-Akoyunoglou, 1970). Such changepresupposes an alteration in the emission spectrum to maintain optimumgrowth conditions.

It is clear that the grow light should allow flexible modification ofspectrum characteristics to enable its use for growing different typesof plants and even modifying spectrum characteristics during thedifferent growth phases. These requirements combined with the idea ofgrowing biomass with a pulsed light source are now tackled with thedisclosed invention.

Two main approaches exist to build a LED source for luminaires used asgrow lights.

In the first approach, the emission spectrum can be generated bycombining optical output of different color discreet LEDs. This type ofhybridized LED structure is often called an RGB LED. In this approachthe LEDs are discreet LED components and e.g. blue-red emissions haveclearly distinct spatial source points. The light is produced within thecompound semiconductor pn-junction while the emission spectrum from asingle pn-junction is relatively narrow, typically only 10 to 40 nm. Dueto narrow emission spectrum several semiconductor chips are used incombination to provide the required wider spectrum to fully cover thered and blue wavelength bands of the visible spectrum required by e.g.photosynthesis. The required semiconductor chips can be packageddiscreetly or mounted inside a same package however optically formingstill a large source point.

In the second approach the emission spectrum is generated within asingle LED package. In this case one or several LED semiconductor chipsexcite wavelength conversion material or typically a phosphor materiallayer to generate continuous emission spectrum matching closely with thephotobiological requirements. For example 425 nm LEDs chip excite anappropriately selected phosphor material layer and can provide typicaldouble peak spectrum offering a relatively good match with the aboveexplained requirements with the primary photobiological process ofphotosynthesis. One such phosphor material is based on nitridoaluminatesand provides an narrow band emission spectrum with full width halfmaximum being only 50 nm or less and matching well the absorptionspectrum of chlorophyll molecules.

In short, commercial light sources, being LED, fluorescent or HPS, allstill commonly apply continuous light with fixed optical spectrum. It isknown that it would be beneficial to apply pulsed light to firstly saveenergy and secondly to apply light source that would enable spectrumadjustment to meet changing spectral requirements during the plantgrowth cycles, or phase of photosynthesis, or to allow use of sameluminaire supporting varying light requirements. Pulsed lightarrangement has been shown to benefit also algae growth (Sforza et al,2012).

PPF (photosynthetic photon flux) should be kept at level similar orequal to sun light level that is roughly 2000 μmols/m²/s to avoid excesslight and stressing plants. Now this applies for continuous light. Withpulsed light the situation changes as the dark cycle can be adjusted sothat the photobiological process has time to ‘use’ the light energyabsorbed during the light cycle. Thus the maximum light intensity can beincreased substantially from nominal sun light level of 2000 μmols/m²/se.g. to 10000 μmols/m²/s to allow even faster growth. However, sucharrangements presumes considering the excess heat from the light source,other growth limiting parameters such as the level of carbon dioxide,and also how to avoid self-shadowing from the canopy to best utilizehigh intensity source.

Artificial grow lights have been under research and delopment fordecades (Olle et al., 2013; Klueter et al. 1980; Yehet al. 2009). Alsopulsed light sources have been introduced earlier (JPS6420034A). Thissource was based on discharge lamps and was able to produce pulselengths between 1 to 50 ms. This early innovation was impaired by thefact that the discharge lamps did not meet well the required spectrumcharacteristics as large part of the light energy is emitted atwavelengths not needed by photobiological processes. Furthermore, thepulse lengths were not short enough to fully exploit the benefits ofpulsed light.

A study carried out by Tennesen with co-workers (Tennessen et al, 1995)shows the benefits of pulsed light. In this study the pulse period of100 μs and dark periods of few ms were used. The experimental lightsource was assembled from discreet LED components emitting at narrowfixed wavelength bands of 658/668 nm only.

First pulsed grow light based on LEDs appears in U.S. Pat. No. 5,012,609(Ignatius). This approach was based on discreet emitters for eachrequired wavelength band i.e. 400-500, 620-680, and 700-760 nm. Thedriving circuit was able to produce pulses in duration of 100 μs, i.e.at optimum length. However, the driving circuit was based oncurrent-limiting-resistor and is considered to have a modest energyefficiency when compared to modern solutions such as the one disclosedin the disclosed invention. The main drawback of the approach was thatit did not provide means to adjust the spectrum for different growthcycles. The spectrum was fixed as the discreet visible range wavelengthemitters were all required to be in the same serial-parallel circuit.

U.S. Pat. No. 5,278,432 (Ignatius) presents some innovations on thepackaging and mounting of discreet LEDs on heat sinking substrate.However, driver circuit is still in the form ofcurrent-limiting-resistor and the spectrum is fixed with all emitterscoupled in series-parallel fashion, excluding the possibility to somehowcontrol the intensity at certain wavelength bands or to adjust theemission spectrum.

WO 02/067660 discloses a system level arrangement of red and white lightLEDs to optimize the emitted spectrum to speed-up the plant growth. Inthe disclosed structure the spectrum is fixed after the discreet LEDshave been mounted on the carrier substrate. It is clear from this andlater publications discussed below that the pulsed light is preferredmode of operation to reduce the total growth time.

The AC driver arrangement disclosed in US2010/244724 (Philips) providesmeans to reduce total cost of the system by applying same driver circuitfor two discreet light sources, emitting in opposite phases of thesinusoidal AC current. Obvious issue becoming the spatial separation ofthe two LED strings to avoid over exposing the plants under and to gainthe benefits of the pulsed lighting.

U.S. Pat. No. 8,302,346 (UoG) discloses a growth enhancing system with afeedback based arrangement applying pulsed light source based again ondiscreet LED chips each emitting a fixed spectrum.

CN 201797809 discloses light source arrangement that applies discreetLED emitters to form the required total spectrum including UV, UVB, blueand near IR.

CN103947470 and CN103947469 disclose light spectrum conditions preferredfor optimum growth of black and red soyabeans, with rough blue, red, andyellow spectrum band ratios being 3:1:5 and 4:3:3 respectively,demonstrating the need for adjustable spectrum type light source toenable wider use for growth of different plants.

CA 2,856,725 discloses hybridized light source arrangement that wouldallow spectrum tunability and pulsed operation mode to preventphotosynthesis saturation. However, the presented light source structurehas a system level approach based on discreet LED components mounted onprinted circuit board with different emission wavelengths, and with afixed ratio of LED emitters at individual wavelength ranges to createrequired spectrum. The expensive feedback system approach based onabsorption and/or fluorescence sensing gives coarse feedback to allowtuning of intensity, and of the light on and off periods i.e. the lightpatterns. However, as the absorption of other than chlorophyll moleculessuch as carotenin molecules, play important role in ‘plant's’ heatsinking capability, and effectively large part of light energy is wastedwhen absorbance is used as a feedback.

WO 20014/188303 discloses means for enhancing plant growth by adjustingthe ratio of blue and red lights alone. US 2014/152194 (Beyer) disclosesanother system to be able to provide necessary spectrum bands forenhancing the growth.

US 2013/318869 has fixed intensity ratios of characteristic peaks atwavelength bands of 400-500 nm (blue), 500-600 nm (green), 600-800 nm(red), and with 500-600 nm band to have lower intensity compared toother two. However, the said arrangement does not allow adjusting theratio between the intensities of the said blue and red wavelength bands.

US 2014/034991 and US 2006/261742 both disclose similar LED arrangementto each other that enable the tuning of the color coordinates and thusthe chromaticity of the light emitted from the LED arrangement. However,these arrangements are not addressing the requirements of biomassgrowing applications or e.g. pulsed light operation. The emissionspectrum is not meeting the photobiological requirements. The operationis defined to be continuous, while not meeting the requirement of havingalternating emission spectrum of pulsed type.

WO2013141824 discloses a similar LED arrangement that enables tuning ofthe spectrum for matching with the chlorophyll b and a absorbance.However, the arrangement is not addressing other requirements of biomassgrowing applications such as the pulsed light operation. The operationis defined to be continuous failing to benefit from alternating emissionspectrum.

SUMMARY OF INVENTION

It is an aim of the present invention to provide a device for achievingbiomass growth.

It is another aim of the present invention to provide a method ofachieving biomass growth.

It is a further aim of the present invention to provide a method ofadjustment of luminaire emission spectrum to allow for predeterminedartificial illumination for different applications in greenhouses or fordifferent growth cycle phases of a same plant.

It is still a further aim of the invention to provide new uses for growlights.

It is still a further aim of the invention to provide a method ofillumination using an integrated light emitting diode (LED) structurewith an adjustable emission spectrum and ability to support pulsed lightemission.

The present invention provides an LED structure comprised of asubstrate, a plurality of optically isolated and electricallynon-independent light emission areas integrated on the substrate, alight emitting semiconductor source of a first type mounted in theemission area(s), and a light emitting semiconductor source of a secondtype mounted in the emission area(s). The LED structure furthercomprises an electrical circuit layer for connecting the light emittingsemiconductor sources in serial fashion for each emission area, and awavelength conversion material of the first type formed on the top ofthe said first type of light emitting semiconductor sources and awavelength conversion material of the second type formed on the top ofthe said second type of light emitting semiconductor sources.

The present invention also provides a method of adjusting the emissionspectrum of the integrated LED structure for photobiological processescomprising the steps of generating the emission output by supplying acommon current to the semiconductor light emitting sources in the LEDstructure; tuning the emission spectrum's multiple intensity peaks to anominal operating point by adjusting the common current value to a midvalue range; and tuning the emission spectrum's multiple peaks'intensity ratios within the full range by adjusting common current froma minimum value to a maximum value.

The method allows for selecting applications requiring emission spectrumwith equal intensity between 620 and 640 nm and between 650 and 670 nmby tuning the common current to a low value within the operating rangeof the integrated LED structure.

The method also allows for selecting application requiring emissionspectrum with high intensity between 620 and 640 nm and low intensitybetween 650 and 670 nm by tuning the common current to a high valuewithin the operating range of the integrated LED structure.

Finally, the method allows for selecting application requiring emissionspectrum with low intensity between 620 and 640 nm and high intensitybetween 650 and 670 nm by tuning the common current to a low valuewithin the operating range of the said integrated LED structure.

Typically, the “low value” of the common current is at least 10%,preferably at least 20%, in particular 30 to 80%, lower than the midvalue of the common current in the range from said minimum value to saidmaximum value, and the “high value” of the common current is at least10%, preferably at least 20%, in particular 30 to 80%, higher than themid value of the common current in the range from said minimum value tosaid maximum value.

Considerable advantages are obtained by the present technology.

Thus, the disclosed integrated LED structure finds use in grow lightsystems previously presented in the art, for example in WO 2013/141824and WO 2009/045107. The disclosed integrated LED structure perfectlysuits grow light systems that are applying various sensors for CO₂, soilhumidity, canopy height, or growth phase to control the illumination bythe feedback from the plants and require dynamic luminaires withadjustable spectrum, tunable intensity and controllable pulse modeoperation.

The disclosed invention also provides an integrated LED structure thatenables flexible usage of one luminaire for a large variety of biomassgrowing applications. The integrated LED structure, with densely packedemission areas, produces high spectral uniformity in the far field,which is difficult to produce with e.g. a discreet LED approach.

Thus, the present integrated LED structure with adjustable emissioncharacteristics will meet the different requirements of various biomassgrowing applications.

No expensive feedback system is needed in the present technology; rathera system approach has been adopted that is based on preset orprogrammable pulse patterns.

BRIEF DESCRIPTION OF DRAWINGS

Embodiments of the present invention will now be further described, byway of non-limiting example, with reference to the accompanyingdiagrammatic drawings.

In the drawings:

FIG. 1 Is a graph representing the relative absorption spectra ofchlorophyll A and chlorophyll B molecules in the wavelength range from400 nm to 700 nm.

FIG. 2 Is a schematic top side view of an integrated LED structureaccording to an embodiment of the present invention.

FIG. 3 Is a schematic view of the cross-section of an integrated LEDstructure according to an embodiment of the present invention.

FIGS. 4A-4B Are graphs representing a typical emission spectrum of anintegrated LED structure according to an embodiment of the presentinvention.

FIGS. 5A-5B Are graphs representing a typical emission spectrum of anintegrated LED structure according to an embodiment of the presentinvention.

DESCRIPTION OF EMBODIMENTS

The following descriptions are merely non-limiting examples and it willbe appreciated by one skilled in the art that specific details of theexamples may be changed without departing from the spirit of theinvention.

It is an aspect of certain embodiments to provide an integrated LEDstructure comprising; a substrate, at least one or a plurality ofisolated emission areas, and an electrical two wire control interface.

In one embodiment, the isolated emission areas comprise one or multipleLED semiconductor diodes as light emitters to provide light emission. Inpreferred embodiments the emitters are of different type and haveemission peaks between 365 to 440 nm.

The light emitters are electrically connected in series to enable acommon current drive scheme. The control interface has at least one wirefor providing the common drive current and least one ground wire toclose the current path back to power supply.

One or multiple isolated emission areas comprise wavelength conversionmaterials to provide means for light emission with wider bandwidth. Oneor plurality of isolated emission areas can comprise in some preferredembodiment more than one type of wavelength conversion materials layeredvertically upon each other.

In preferred embodiments the wavelength conversion material is a narrowband phosphor based e.g. on nitridoaluminates materials providingemission spectrum with full width half maximum of 40 to 80 nm.

The isolated emission areas can be formed as buried shallow cavities onthe top surface of the said substrate. Alternatively, the isolatedemission areas can be formed by manufacturing an optically opaque mesastructure between the emission areas. In some preferred embodiments theLED structure can comprise both buried shallow cavities and isolatedemission areas surrounded by opaque mesa structure. In some preferredembodiments the LED structure can comprise several emission areas inburied cavities of different heights.

The emission spectrum is formed of emissions from different emissionareas at wavelength bands with at least some of them in blue (365-440nm) and red (600-780 nm) bands and optionally having one or multipleemission bands in wavelength bands of ultra-violet (UV), green, red andnear-infra red to complement the emission spectrum.

In some embodiments the emission side of the integrated LED structurecan be equipped optionally with a polarizer to provide polarized lightdepending again the lighting and application requirements. The saidpolarizer can cover all or some of the emissions areas.

An embodiment comprises using an integrated LED structure, which has twodifferent type of semiconductor emitters coupled in series and which isdriven with a common current signal. The light emitters have differentcurrent-to-light conversion due to different thermal characteristics.This results in asymmetric excitation of the wavelength conversionmaterial with high current values due to elevated operating temperature.

In more detail, the asymmetric excitation can be explained as follows:

In a nominal operation point the current is e.g. 350 mA and the emissionspectrum has a characteristic quadruple structure with blue emissionse.g. at 425 nm and 435 nm, and one red (red1) emission peak at 630 nmand another red (red2) emission peak at 660 nm. The said intensity ratiobetween the blue1:blue2:red1:red2 is in low current state close to e.g.1:1:2:2. In another set point of operation, also known as the “highcurrent state”, the current is tuned up to e.g. 700 mA. Now the otherlight emitter, namely the sapphire based light emitter shows reducedemission efficiency with relative to vertical type emitter and thecharacteristic quadruple peak structure changes so that the intensityratio of the four peaks become close to 2:1.5:4:3. Such spectrum tuningis beneficial for optimizing the artificial lighting conditions fordifferent growth phases of various plants in greenhouse.

In one embodiment, the intensity ratio between a peak in the range of620 to 640 nm and a corresponding peak in the range from 650 to 670 nmis in the range from about 0.8:1 to 3:1.

In another embodiment, the intensity ratio between said peaks is in therange from about 0.5 to 1.1:1 as a low value of intensity and in therange from about 1.2 to 3:1 at a high value of intensity.

In general the isolated emission areas can be driven via the controlinterface intermittently to turn on and off, also called later asactivation, to provide a light energy pulse of required length. A turnoff time, also called later as a delay time or deactivation time, withno light emitting from the emission area can be controlled via themultiple wire control interface. Furthermore, the current control allowsdeactivation of the emission area for longer periods. Also the currentcontrol allows setting of emission frequency of emission area to providethe required spectral density, as required by arbitrary biomass growingapplication.

Appropriate electrical current control sequence via the controlinterface allows generating emission spectrum which is varying in time.

Embodiments of the invention provide further interesting features andadvantages.

In one preferred embodiment the integrated LED structure providesbuilt-in spectrum adjustability based on a common drive current ofasymmetric excitation arrangement. The integrated LED structure isformed of two isolated emission areas in a way that the emission fromthe first emission area does not influence the emission from the otheremission area. In such arrangement of two emission areas the firstemission area applies the first type of excitation source and the firsttype of wavelength conversion material.

Consistently, the second emission area applies the second type ofexcitation source and the second type of wavelength conversion material.The asymmetric excitation is thus achieved by applying two differenttypes of excitation sources, buried under the wavelength conversionmaterials in the two isolated emission areas, and connected electricallyin series with each other to be able to control them simultaneously witha common drive current.

In a typical case the first wavelength conversion material is a wideband phosphor with excitation maximum near 420 nm and emission maximumnear 630 nm, and FWHM of about 100 nm and the second first wavelengthconversion material is a wide band phosphor with excitation maximum near435 nm and emission maximum near 660 nm, and FWHM of about 100 nm.

The first type of the excitation source is a so called vertical lightemitting semiconductor diode operating e.g. at 420 nm, and the secondtype of excitation source is a sapphire based light emittingsemiconductor diode operating e.g. at 435 nm.

The two types of the semiconductor diodes have different thermalbehavior, and their light output varies independently as a function ofjunction temperature, which on the other hand depends of the drivecurrent.

Typically the sapphire based semiconductor diode's light output dropsfaster as a function of rising junction temperature while the verticalsemiconductor diode structure is relatively insensitive to junctiontemperature, as long as the junction temperature is kept withinpreferred operating range i.e. typically between 45 to 90° C. In anominal situation the combination of the two semiconductor diode typesis driven with a common 300 mA current producing an excitation spectrumat blue wavelengths of 425 and 435 nm (FIG. 4) with a 1:1 intensityratio between 420 nm and 435 nm. This results in nearly equal emissionpeaks at 630 and 660 nm from the two phosphors. As the current isincreased to 700 mA the efficiency of the sapphire LED drops and theoutput spectrum changes accordingly while changing the intensity ratioof blue excitation to roughly 1:0.75. This in turn results in anemission intensity ratio of 630 nm and 660 nm to change to 1:0.75.

This characteristic behavior can be applied also gradually by tuning thecurrent continuously or stepwise between 300 mA and 700 mA, thusenabling the adjustment of the said ratio of excitation intensities at420 nm and 435 nm wavelengths from 1:1 to 1:0.75 and adjusted spectrumof red wavelength bands, following the excitation intensities. So anywanted intensity ratio can be set in a flexible way by adjusting thecommon drive current.

In another preferred embodiment the integrated LED structure providesbuilt-in spectrum adjustability by applying narrow band phosphorsmatching the absorption spectrum of chlorophyll A and chlorophyll B.

In one case there are two emission areas, which have differentwavelength conversion materials, for example the first emission area hasa narrow band phosphor of the first type providing peak output at 630 nmwith and the second emission area has a narrow band phosphor of thesecond type providing peak output at 660 nm (FIG. 5). Such narrow bandphosphors could be of e.g. nitridoaluminates based material providingemissions with full width half maximum of typically only 50 nm and theiremission spectrum suits particularly well for the excitation of thechlorophyll molecules. In such case the first emission area appliesvertical type LED chip and the second emission area applies a sapphirebased LED chip. Now it becomes straightforward to adjust the ratio of630 and 660 nm emission of the integrated LED structure by simply tuningthe common drive current.

Narrow bandwidth red phosphors are used for red wavelength areaselective excitation of chlorophyll A and chlorophyll B in order tominimize chlorophyll A and chlorophyll B bands over lapping as well tomaximize individual chlorophyll A and chlorophyll B absorption bandcoverage. Narrow bandwidth red phosphor should have emission peakbetween 600-700 nm and peak's full width half maximum value less than 50nm but more 25 nm or more preferably less than 50 but more than 35 nm.

The asymmetric excitation and the common current drive method can beapplied also in case there is a plurality of isolated emission areas. Insuch case the number of different type of excitation sources and thenumber of different type of wavelength conversion materials is notnecessarily two.

Furthermore the asymmetric excitation and the common current drivemethods can be applied in case there is only one emission area. In suchcase the number of different type of excitation sources can be e.g. twoand the emission area comprises one type of wavelength conversionmaterial.

Turning next to the embodiment shown in FIGS. 2 to 5, the following canbe noted:

The LED structure is comprised of a substrate 100, two opticallynon-interacting isolated emission areas 101, and 102, and a two wirecontrol interface 103, see FIG. 2. The first emission area 101 comprisesthe first type of LED semiconductor chip 104 emitting at 425 nm, andwavelength conversion material 105 having its peak emission at 630 nmand having a full width half maximum (FWHM) emission of about 50 nm. Thesecond emission area 102 comprises a second type of LED semiconductorchip 106 emitting at 438 nm, and wavelength conversion material 107having its peak emission at 660 nm and having a full width half maximum(FWHM) emission of about 50 nm.

The first LED chip is of vertical type and the second one is of sapphirebased LED chip. The control interface is having a two wire structure andis to enable common control of the said two isolated emission areas. Thetwo emitter diodes are connected in series to enable a common drivecurrent control. Thus the cathode of the first emitter diode, located inthe first emission area, is connected to the anode of the second emitterdiode, located in the second emission area. One electrical contact pointof the control interface is electrically connected to the anode of thefirst emitter diode in the first emission area, and the other electricalcontact point is electrically connected to the cathode of the secondemitter diode in the second emission area. Thus a close current loop isformed with the said two emitter diodes in series, enabling a commoncurrent drive for applying the asymmetric excitation scheme.

The optically independent operation of the two isolated emission areasis achieved by isolating the said first emission area from the secondemission area with an optically opaque mesa structure 113, whichprevents light emission from the LED emitter 104 located inside of thefirst emission area 101 to excite the wavelength conversion material 107inside the said second emission area. The mesa structure 113 a is shownin FIG. 3 in the cross section view of the said LED structure.

The first emission area and the second emission areas provide two redwavelength bands centered at 630 and 660 nm and contribute to the totalemission spectrum. The emission band centered at 630 nm is used for theexcitation of chlorophyll B and emission band centered at 660 nm is usedfor the excitation of chlorophyll A. The emission spectrum is adjustableand can be controlled by tuning of the common continuous drive currentso that the ratio of the 630 and 660 nm intensities vary in scale of 1:1to 1:0.75. Such magnitude of change can be expected with a currenttuning range of 350 mA to 700 mA.

The integrated LED structure described in the previous embodiment can beoptionally powered by pulsed source to optimize the excitation of thechlorophyll molecules associated with plants' photosynthesis process.The said LED structure is driven alternately with a pulsed currentsequence with a pulse on time period being 0.1 ms and off-time being 2to 10 ms.

FIGS. 4 a, 4 b, 5 a and 5 b were already referred to above. In summaryit can be noted that FIGS. 4a and 4b show the nominal emission spectraof LED module with two isolated emission areas comprised of asymmetricexcitation emitters at 425 nm and 435 nm driven at common current of 350mA (left) and 700 mA (right). Emission areas comprise wide band phosphormaterial with FWHM of about 100 nm. Red emissions are not summed forvisualization purposes.

FIGS. 5a and 5b show the nominal emission spectrum of LED module withtwo isolated emission areas comprised of asymmetric excitation emittersat 425 nm and 435 nm driven at common current of 350 mA (left) and at700 mA (right). Emission areas comprise narrow band phosphor materialwith FWHM<60 nm. Red emissions at 630 and 660 nm are not summed forvisualization purposes.

It is to be understood that the embodiments of the invention disclosedare not limited to the particular structures, process steps, ormaterials disclosed herein, but are extended to equivalents thereof aswould be recognized by those ordinarily skilled in the relevant arts. Itshould also be understood that terminology employed herein is used forthe purpose of describing particular embodiments only and is notintended to be limiting.

Reference throughout this specification to “one embodiment” or “anembodiment” means that a particular feature, structure, orcharacteristic described in connection with the embodiment is includedin at least one embodiment of the present invention. Thus, appearancesof the phrases “in one embodiment” or “in an embodiment” in variousplaces throughout this specification are not necessarily all referringto the same embodiment.

As used herein, a plurality of items, structural elements, compositionalelements, and/or materials may be presented in a common list forconvenience. However, these lists should be construed as though eachmember of the list is individually identified as a separate and uniquemember. Thus, no individual member of such list should be construed as ade facto equivalent of any other member of the same list solely based ontheir presentation in a common group without indications to thecontrary. In addition, various embodiments and example of the presentinvention may be referred to herein along with alternatives for thevarious components thereof. It is understood that such embodiments,examples, and alternatives are not to be construed as de factoequivalents of one another, but are to be considered as separate andautonomous representations of the present invention.

Furthermore, the described features, structures, or characteristics canbe combined in any suitable manner in one or more embodiments. In thefollowing description, numerous specific details are provided, such asexamples of lengths, widths, shapes, etc., to provide a thoroughunderstanding of embodiments of the invention. One skilled in therelevant art will recognize, however, that the invention can bepracticed without one or more of the specific details, or with othermethods, components, materials, etc. In other instances, well-knownstructures, materials, or operations are not shown or described indetail to avoid obscuring aspects of the invention.

While the forgoing examples are illustrative of the principles of thepresent invention in one or more particular applications, it will beapparent to those of ordinary skill in the art that numerousmodifications in form, usage and details of implementation can be madewithout the exercise of inventive faculty, and without departing fromthe principles and concepts of the invention. Accordingly, it is notintended that the invention be limited, except as by the claims setforth below.

INDUSTRIAL APPLICABILITY

The present arrangements and methods can be used for providingartificial grow light in greenhouses as well as in other objects inagriculture, horticulture and in biomass growing industry, in particularfor meeting the needs of different plants to achieve optimal growth.

REFERENCE SIGNS LIST

-   100 substrate-   101, 102 first and second emission areas-   103 wire control interfaces-   104 first type of LED semiconductor chip-   105, 107 wavelength conversion material-   106 second type of LED semiconductor chip-   113 optically opaque mesa structure-   113 a mesa structure

CITATION LIST Patent Literature

-   CN103947470A-   CN103947469A-   WO2013141824A1-   WO2009045107A1-   JPS6420034A-   U.S. Pat. No. 5,012,609-   U.S. Pat. No. 5,278,432-   WO02067660A1-   US2010244724A1-   U.S. Pat. No. 8,302,346-   CN201797809-   CA2856725A1-   WO2014188303A1-   US2013318869A1-   US2014152194A1-   US2014034991A1-   US2006261742A1

Non-Patent Literature

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The invention claimed is:
 1. A method of adjusting the emission spectrum of an integrated LED structure for photobiological process, comprising: generating the emission output by supplying a common current to the semiconductor light emitting sources in the LED structure; tuning the emission spectrum's multiple intensity peaks to a nominal operating point by adjusting the common current value to a mid-value range; and tuning the emission spectrum's multiple peaks' intensity ratios within the full range by adjusting the common current from a minimum value to a maximum value.
 2. The method of claim 1, further comprising tuning the common current to a low value within the operating range of said integrated LED structure in order to achieve an emission spectrum with equal intensity between 620 and 640 nm and between 650 and 670 nm.
 3. The method of claim 1, further comprising tuning the common current to a high value within the operating range of said integrated LED structure in order to achieve an emission spectrum with high intensity between 620 and 640 nm and low intensity between 650 and 670 nm.
 4. The method of claim 1, further comprising tuning the common current to a low value within the operating range of said integrated LED structure in order to achieve an emission spectrum with low intensity between 620 and 640 nm and high intensity between 650 and 670 nm.
 5. The method according to claim 2, wherein the low value of the common current is at least 20% lower than the mid value of the common current in the range from said minimum value to said maximum value.
 6. The method according to claim 3, wherein the high value of the common current is at least 20% higher than the mid value of the common current in the range from said minimum value to said maximum value.
 7. The method according to claim 1, wherein the intensity ratio between a peak in the range of 620 to 640 nm and a corresponding peak in the range from 650 to 670 nm is in the range from 0.8:1 to 3:1.
 8. The method according to claim 7, wherein the intensity ratio between said peaks is in the range from 0.5 to 1.1:1 as a low value of intensity and in the range from 1.2 to 3:1 at a high value of intensity.
 9. The method according to claim 1, wherein the LED structure comprises: a substrate; a plurality of optically isolated and electrically connected light emission areas integrated on the substrate; a light emitting semiconductor source of a first type mounted in the emission area(s); a light emitting semiconductor source of a second type mounted in the emission area(s); an electrical circuit layer for connecting the said light emitting semiconductor sources in serial fashion for each emission area; a wavelength conversion material of the first type formed on the top of the said first type of light emitting semiconductor sources; and a wavelength conversion material of the second type formed on the top of the said second type of light emitting semiconductor sources. 